Among the several approaches that have been or are being used to reduce pollution of the atmosphere caused by the automotive internal combustion engine is a system that injects air obtained from an air pump into the exhaust system of the engine. This injected air aids further combustion of the gases which are exhausted by the engine, thus reducing the pollutants discharged into the atmosphere. In some of the more recent proposals these pollutants can be further eliminated by passing the exhaust gases through a catalytic converter. Whether a catalytic converter be used or not, additional air to supply the necessary oxygen for combustion is mandatory.
Control of the air injected into the exhaust system has been found to be necessary in order to avoid certain undesirable consequences. For example, most air pumps used in the type system here involved are belt-driven from the engine. These pumps, being of the positive displacement type, deliver increasing volumes of air at frequently increasing pressures as the speed of the engine is increased. Since only a certain amount of additional oxygen, by way of injected air, is necessary, it is often desirable that the quantity of air be kept within certain maximum limits. Also, it is desirable that the pressure in the air system be held within reasonable limits in order to avoid unnecessary stresses on the pump and the imposition of additional horsepower requirements upon the engine. Moreover, in those systems utilizing catalytic converters, it is advisable to limit the air injected during certain modes of operation to prevent overheating and consequent destruction of the catalyst system. It is frequently desired to terminate air injection into the exhaust system whenever the engine is operating under very heavy load conditions, when manifold vacuum is very low and also to reduce or eliminate air injection if there is any loss of manifold vacuum caused by any malfunction or damage to any part of the system.
Pressure relief and air by-pass valves are known and an example of such a valve is disclosed in the to Crawford et al, U.S. Pat. No. 3,520,320, dated July 14, 1970. Such valves have performed very satisfactorily for their intended purpose, but do not fully meet all of the newer requirements that are presently being imposed as overall emissions technology changes.
Accordingly, among the objects of the present invention are to provide a by-pass and pressure relief valve for the air injection system of an automotive internal combustion engine. An additional object of the invention is to make provision for exhausting or venting excess air without interrupting or unduly reducing air delivery to the engine exhaust system.